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Historic Journey. Remarkable as those photographs were, they tended for a few excited moments to hide the rest of a remarkable feat. Without a single snapshot to show for its travels, Mariner IV would still have earned its place in the annals of science. In its 325-million-mile, 228-day flight, it had charted interplanetary reaches never before explored by man and set an impressive record for long-distance communication. All during its trip, Mariner sent back valuable scientific information about the solar wind, cosmic dust, magnetic fields and deep-space radiation. In the vicinity of the red planet it scouted the hazards that astronauts will meet when they try to land there. It gave earthbound experts their most accurate estimates of the planet's structure and mass; it beamed radio signals through the Martian atmosphere to study its density and looked for signs of a magnetic field.
Mariner started its historic journey on Nov. 28, 1964, only three weeks after Mariner III failed because it could not jettison its protective shroud. A powerful Atlas-Agena rocket lofted the 575-lb. Mariner IV through Earth's atmosphere, then kicked it loose to take off on its own like a great flying windmill. The spacecraft, freed from a cocoon-like covering, unfolded the four solar panels that powered its instruments by converting the sun's energy into electricity. With those panels deployed, it measured 22 ft. 7½ in. across and 9½ ft. to the top of its antenna. Curving into a wide-swinging, elliptical orbit that was precisely plotted in advance, the ship set out to intersect the orbit of Mars at a predetermined time.
The ship was a space scientist's dream laboratory—crammed to capacity. Its four panel blades shone purple from the thin sapphire-glass coating that protects their 28,224 tiny solar cells from radiation damage. Its silvery octagonal body, made of magnesium and aluminum alloy, carried 138,000 components, including 31,696 delicate electronic components ranging from a computer to a small, lO½-watt radio transmitter. It was programmed and equipped to send to Earth a continuous stream of reports on 39 scientific and 90 engineering measurements. Crowded into the spacecraft were a new type of helium gas magnetometer to study magnetic fields, an ionization chamber and Geiger counter to measure galactic cosmic rays, a collector cup to measure the solar wind's barrage of protons, a cosmic-ray telescope and cosmic-dust collector —plus the all-important TV camera. "I don't think you could improve the payload," said one of the project scientists. "It's a damn near perfect mix of experiments."